The present invention relates generally to liquid transfer systems and in particular the present invention relates to liquid transfer valves for measuring and dispensing precise volumes of samples in a hematology or blood analyzer.
Liquid transfer valves have been used to measure and dispense precise microliter volumes of samples. One type of transfer valve is a rotary operating type having a pair of measuring chambers established in a series coupled relationship which is capable of providing simultaneously a pair of precisely measured, different liquid volumes and directing each to a pair of different predetermined locations, each along with a respective known volume of diluent.
U.S. Pat. No. 4,507,977 issued Apr. 2, 1985 describes a rotary valve assembly comprising a pair of stationary outer disc members and a rotary inner disc sandwiched therebetween and engaged with the interior faces of both outer discs. A hollow external loop is secured to one of the outer discs and a segmenting passageway is provided in the inner disc and constitutes a first measuring chamber. The loop secured to the outer disc constitutes a second measuring chamber. The valve assembly operates between two conditions, load and delivery. The valve assembly has a single sample input connection that is coupled to an external switch. The external switch allows for the selection of either a first or second sample.
The external switch can be designed in different configurations. For example, a hematology analyzer called Advia manufactured by Bayer uses a rotary 3-way valve to switch two sample inlet ports. External switches often require excess amounts of blood samples, which can be critical for baby blood samples. As an alternative to the rotary valves, a CD3500 blood analyzer manufactured by Abbott Laboratories uses two pinch valves to switch between two sample fluids. While reducing sample volumes, this system may cause the analyzer to carry air bubbles inside of the blood sample. Additional examples are provided in Sysmex hematology analyzers SF-3000 and XE-2100, which have duplicated shearing holes on one set of sample shearing valves and one sample probe directly attached to one of the three valves to avoid having an external switching valve. Such valve systems make instrumentation complicated due to the necessity to double (xc3x972) associated valves around the sample shearing valve.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for a liquid metering and transfer valve that reduces sample volume and external sample switching. The above-mentioned problems with liquid metering and transfer valves and other problems are addressed by the present invention and will be understood by reading and studying the following specification.
In one embodiment, a liquid metering and transfer valve assembly comprises first and second stationary valves and a rotatable inner valve sandwiched between the first and second valves. The inner valve has opposite surfaces sealingly engaged with adjacent surfaces of the first and second valves. A rotatable port switch is located adjacent to the first valve, such that the first valve is sandwiched between the inner valve and the port switch. The port switch has a surface sealingly engaged with an adjacent surface of the first valve, wherein the port switch comprises first and second input connections to receive externally provided fluids.